The overall objectives are: a) to determine the early and sequential structural events of RNA virus-induced neoplastic transformation of the glioblasts of the subependymal plate, b) to determine if the subependymal cell plate of the developing mammalian brain is the source of the neoplastically transformed cells which give rise to the glioma group of brain tumors and, c) to determine the fate of the viral genome within the transformed glial cells. APPROACH: Neonatal dogs are inoculated intracerebrally with 0.0l cc of high titer Avian Sarcoma Virus. Glial tumor yield is 100% within four weeks. The early and sequential structural events of the viral transformation are studied by serial sacrifice of animals, at intervals after inoculation, with appropriate controls. Gliomas can be identified, in relationship to the subependymal cell plate, by the 10th day after inoculation. These gliomas are structurally similar to those which occur in symptomatic animals at four weeks. The subependymal plate is pulse-labeled with tritiated thymidine concomitant with viral inoculation; the transformed cells, which undergo a series of morphological alterations observable within 17 minutes after viral inoculation, are thereby identified and their patterns of migration and the ultimate formation of a tumor mass is therefore amenable to structural analysis using transmitted light, differential interference optics, and electron microscopy. BIBLIOGRAPHIC REFERENCES: Vick, N. A. and Bigner, D. D.: Early and sequential events of the neoplastic transformation of glia by Avian Sarcoma Virus: in vivo studies in the neonatal dog. In: Proc. VII International Congress of Neuropathology, pp 437-444, Elsevier, Amsterdam, 1975. Yung, W.-K and Vick, N.A.: "Glioblastoma", Induction of a reproducible autocthonous tumor in rats with murine sarcoma virus. Neurology 26:76-88, 1976.